A1 and A2 adenosine receptor regulation of erythropoietin production

The effects of adenosine (ADE) and ADE agonists on erythropoietin (Ep) production were determined using percent (%) 59Fe incorporation in red cells of exhypoxic polycythemic mice. The hemisulfate salt of ADE produced a significant increase in % 59Fe incorporation in response to hypoxia in concentrations of 400 to 1600 nmol/kg/day (i.v.). 5'-N-ethyl-carboxamideadenosine (NECA), a selective A2 receptor agonist, increased radioiron incorporation in a dose-dependent manner (10-100 nmol/kg/day, i.v.). In contrast, N6-cyclohexyladenosine (CHA), a selective A1 receptor agonist, did not affect radioiron incorporation in concentrations up to 1600 nmol/kg/day (i.v.). Albuterol, a beta 2-adrenergic agonist, enhanced % 59Fe incorporation in polycythemic mice and low doses of CHA (50 and 100 nmol/kg/day), which were not effective alone on % 59Fe incorporation in polycythemic mice exposed to hypoxia, inhibited the enhancement in radioiron induced by albuterol (25 and 100 micrograms/kg/day, i.p.) plus hypoxia. Theophylline (20 and 80 mg/kg/day, i.p.), a well-known antagonist of ADE receptors, blocked the ADE and NECA enhancement in radioiron incorporation at a dose of theophylline alone which produced only a slight enhancement of % 59Fe incorporation. These results suggest that ADE may both inhibit through A1 receptor activation and increase via A2 receptor stimulation the production of Ep.